(1) Field of the Invention
This invention relates to a method for catalytically dewaxing hydrocarbon oil, and more particularly to a method for producing hydrocarbon oil of good flowability by thermally contacting such hydrocarbon oil represented by petroleum fraction with zeolite system catalyst.
(2) Description of the Prior Art
Recently, demand for B and C heavy fuel oils has been reduced, though that for so-called middle distillate involving kerosene, gas oil, and A heavy fuel oil has been increased. As a manner for responding to such demand, there is a method wherein the end point in the distillation test of gas oil fraction has been set higher, whereby yield of gas oil is elevated. In this case, however, the pour point thereof rises also with the increase in the end point, so that problems arise in the properties of the product. In this connection, it becomes necessary for providing such a process that the pour point of the gas oil fraction having a high pour point thus obtained is made to decrease to use the same as a compounding ingredient for gas oil or A heavy fuel oil.
On the other hand, there is an increasing demand for a lubricating oil fraction having a low pour point and a low viscosity as a base oil for insulating oil, refrigerating oil, hydraulic oil and the like.
These oils have heretofore been obtained by fractional distillation or purification of naphthenic crude oil of low wax content, but the remarkable demand for the former oils continues to expand so that there is a necessity of searching for other sources of the raw material.
Lubricating oil fraction having the above mentioned property may be obtained from abundant paraffinic crude oil in accordance with the solvent dewaxing method, but such manner involves a problem from viewpoint of cost so that a more inexpensive method is desired.
In addition, when this solvent dewaxing method is used, the pour point of the obtained base oil for lubricating oil is within the range of about -34.degree. C. to about 0.degree. C. Therefore, the solvent dewaxing method cannot substantially manufacture the specific lubricating oil in which a lower pour point than -34.degree. C. is required, under mild conditions and at a low energy cost.
In view of the above, various catalytic dewaxing methods have been proposed as those for lowering pour point of hydrocarbon fraction.
For example, there are disclosed Japanese Patent Publication No. 31856/1970 wherein mordenite is used as the catalyst, Patent Publication Nos. 30463/1970 and 7764/1972 in which type A zeolite is utilized as their catalysts, Patent Publication No. 32723/1972 wherein erionite is used as the catalyst, and Patent Publication No. 34444/1974 in which ZSM-5 zeolite is used as the catalyst, respectively. However, these prior art methods involve such disadvantages of not so high recovery, short catalyst life and the like. Thus, development for such catalysts having high selectivity and long life is desired.
Further, in order to use a dewaxed oil as the base oil for lubricating oil, it is required that the dewaxed oil is excellent in viscosity index, oxidation stability and the like. In this point, the conventional catalytic dewaxing techniques cannot provide the base oil for lubricating oil having a sufficiently satisfactory performance, and hence it is demanded to eliminate this drawback through the development of catalysts.